1. Field of the Invention
This invention relates to an engine valve actuating system for an outboard motor and more particularly to an improved arrangement for achieving variable valve actuation (timing and/or lift) in the operation of an engine valve.
2. Description of Related Art
There is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued increase in power output in outboard motors. Accordingly, four-cycle engines have started to replace two-cycle engines in outboard motors. It is difficult, however, to arrange all the components of a four-cycle engine into the limited space of an outboard motor cowling.
It is also desirable to achieve good emission control, fuel economy and high power output over the entire speed and load ranges of the outboard motor. In automotive four-cycle engines, there have been proposed a wide variety of devices to permit the engine characteristics to be adjusted when running so as to obtain optimum performance across the entire speed and load range. One such device is a variable valve actuating mechanism, which includes both changing valve timing and/or the valve lift. However, variable valve actuating mechanisms are typically complex and are not compact. Accordingly, because of the size constraints of an outboard motor, it previously has been difficult to employ variable valve actuating mechanisms in an outboard motor.
A need therefore exists for an engine with a variable valve actuating mechanism that is simply constructed and compact in structure.
One aspect of the present invention involves an engine comprising an output shaft and at least one cylinder having a cylinder axis. The output shaft and the cylinder are arranged such that a central plane, which contains the cylinder axis, either lies parallel to or contains an axis about which the output shaft rotates. A plurality of ports communicating with the cylinder and a plurality of valves selectively open and close the ports. At least a first valve is disposed on a first side of the central plane and at least a second valve is disposed on a second side of the central plane. A valve actuating mechanism comprises a camshaft having a plurality of cams and a pair of adjacent first and second rockers. A first support pivotally supports the first and second rockers. Each rocker has cam side arm with a following surface engaged with one of the cams to pivot the rocker about the first support. The first rocker has first and second bores and cam side arm with an operator that directly engages the first valve. The first bore slideably supports a first member and the second bore slideably supports a second member. The first support includes a first passage that communicates with the second bore. The second rocker further includes a first engagement surface that engages the first member. The second member is arranged to engage the first member when an actuating pressure is supplied to the first passage such that movement of the second rocker is transmitted to the first rocker. The valve actuating mechanism also includes at least a third rocker. The third rocker has cam side arm with a following surface, which engages another one of the cams to pivot the third rocker about a second support, and a valve side arm with an operator that directly engages the second valve.
Another aspect of the present invention involves an engine including a valve actuating mechanism comprising a camshaft with at least two adjacent intake cams and at least one exhaust cam. An intake rocker support supports a pair of adjacent, pivotally-supported first and second intake rockers. Each intake rocker has a cam side arm with intake following surface that is engaged with one of the intake cams for pivoting the intake rocker about the intake rocker support. The first intake rocker has a cam side arm with an operating portion that directly engages an intake valve of the engine. A first member is slideably supported within a first bore of the first intake rocker, a second member is slideably supported within a second bore of the first intake rocker. A first passage is located within the intake rocker support and communicates with the second bore. The second intake rocker further includes a first engagement surface that engages the first member. The second member selectively engages the first member when an actuating pressure is supplied to the first passage such that movement of the second intake rocker is transmitted to the first intake rocker. The valve actuating mechanism additionally comprises at least one exhaust rocker having a cam side arm with an exhaust following surface engaged with the exhaust cam for pivoting the exhaust rocker about an exhaust rocker support. The exhaust rocker support lies generally parallel to the intake rocker support and is on a side of the camshaft opposite the intake rocker support.
In accordance with an additional aspect of the present invention, a valve actuating mechanism is provided for an engine. A camshaft is located inside a cam cover and is driven by a crankshaft of the engine. The camshaft includes a plurality of cams. An intake rocker shaft extends along one side of the camshaft and an exhaust rocker shaft extends along generally an opposition side of the camshaft inside the cam cover. Intake and exhaust rockers are supported by the respective intake and exhaust rocker shafts for transmitting cam rotation to corresponding valves of the engine. Means is provided to selectively couple one of the valves to one of a pair of adjacent cams on the camshaft. The cams of the pair have the cams of the pair have different shapes to vary an operating characteristic of the corresponding valve. In one preferred mode, the cams have different lifts.
Additional aspects, features and advantages will be understood by the following description of several preferred embodiments of the present engine.